The present invention relates to disposable absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like, and in particular to the control of their hydration effect on the human skin.
Disposable, absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like are well know in the art. Typically, disposable absorbent articles comprise a liquid previous topsheet that faces the wearers body, a liquid impervious backsheet that faces the wearers clothing, an absorbent core interposed between the liquid previous topsheet and the backsheet, and means to keep the core in fixed relation to the wearers body.
The absorbent core needs to be capable of acquiring, distributing, and storing discharges initially deposited on the topsheet of the absorbent article. Preferably the design of the absorbent core is such that the core acquires the discharges substantially immediately after they have been deposited on the topsheet of the absorbent article, with the intention that the discharges do not accumulate on or run off the surface of the topsheet, since this may result in inefficient fluid containment by the absorbent article which may lead to wetting of outer garments and discomfort for the wearer. After the insult, it is an essential functionality of the absorbent article to retain the discharged fluids firmly so as to avoid over-hydration of the skin of the wearer. If the absorbent article is not well functioning in this respect, liquid coming from the absorbent core back to the skinxe2x80x94also often called xe2x80x9crewetxe2x80x9dxe2x80x94can have detrimental effects on the condition of the skin, which can for example be observed by skin irritations.
There, have been many attempts to improve the fluid handling properties of absorbent articles or cores, in particular when further requirements were brought up such as a desired reduction of product bulkiness or thickness.
Several patent publications deal with such improvements by adding specially treated cellulosic material. For example U.S. Pat. No. 4,898,642 of Moore et al. discloses specially twisted, chemically stiffened cellulosic fibres and absorbent structures made therefrom. EP 0 640 330 (Bewick-Sonntag) et al. discloses the use of such fibres in a specific arrangement with specific superabsorbent materials. EP 0 397 110 (Latimer) discloses an absorbent article comprising a surge management region for improved fluid handling, having specific basis weights, acquisition times and residual wetness.
EP 0 312 118 (Meyer) discloses an absorbent article with a fibrous topsheet with larger pores than the pores of the underlying transport layer, which in turn has larger pores than the underlying absorbent body. Further, the transport layer has to have a hydrophilicity which is less than the one of the absorbent core, and may generally be characterized as being substantially hydrophobic.
In EP 0 312 118 it is said that some liquid might remain in the transport layer and in the topsheet, so as to cause a wet feel on the surface. In order to overcome this problem, it is proposed in EP 0 312 118 to exploit the resilient compressibility of the transport layer, such that in use under the pressure exerted by the baby, the pores become smaller and then can dry out the topsheet and transport the fluid away into the underlying absorbent body.
In accordance with the development direction of these various approaches, the tools to assess the performance of such structures were generally aiming at measuring the liquid transferxe2x80x94either from the surface of the absorbent structure into the structure itself often referred to as the acquisition, or within the absorbent structure referred to as distribution.
On the other hand the rewetting from the absorbent structure has been tested, either by using in-vivo methods or by using laboratory tests.
The in-vivo methods have in common, that they assess directly the condition of the skin of the wearer of an absorbent article either under real in-use loadings or possibly with artificially loaded articles, which are for example worn on the forearm of a test person for a certain period.
Elsner et al. provides a comprehensive overview of such methods in xe2x80x9cBio-engineering of the: Water and Stratum Corneumxe2x80x9d, CRC Press, 1994. The most relevant methods are the xe2x80x9cTransepidermal Water Lossxe2x80x9d (often abbreviated TEWL) measuring the moisture evaporation from the skin; methods to measure the electrical properties like capacitance, impedance, or conductance of the skin, which depend strongly on the moisture content, such as with the NOVAMETER (capacitance of skin) the CORNEOMETER or other instruments. Elsner further discusses in detail the negatives of both too dry and too wet (overhydrated) skin, and the risks of higher occurrence of skin irritations or even damages, which can be most easily detected by xe2x80x9credmarkingxe2x80x9d of the skin, in particular, when the over-hydration occurs in combination with mechanical stress such as chafing.
However, all in-vivo methods have in also common, that the comparison of absorbent structures or articles for development purposes is cumbersome. Apart from the fact of needing test persons as such, individual parameters of the test personsxe2x80x94such as varying reaction to certain room conditions as temperature or relative humidityxe2x80x94are responsible for a large variability in the test results. In order to still get meaningful data, the number of test persons must be increased to substantial amounts.
Hence, significant effort has already been put against evaluating absorbent articles and structures under reproducible and easy to execute laboratory conditions, whereby mostly the human skin is replaced by standardized fluid pick-up filter paper. Essentially, these methods are based on the xe2x80x9ccapillary rewetxe2x80x9d principle, whereby a test sample is loaded with a certain amount of test fluid, such as synthetic urine. After a certain time such as to allow for equilibration and preferably under a certain pressure, the pick up filter paper as xe2x80x9cskin replacementxe2x80x9d is placed on top of the surface of the loaded structure for a certain time, under a certain pressure. The pick-up filter paper is well defined such as by porosity, basis weight, or absorbency. Due to the capillary forces of its pores, it is sucking up readily available moisture (i.e. xe2x80x9cfreexe2x80x9d moisture not being bound such as through superabsorbent materials or in smaller pores than the ones of the pick-up paper) from the surface of the test specimen and the weight increase is a measure for the xe2x80x9crewetxe2x80x9d performance of the absorbent article.
Optionally, this test procedure can be combined with other fluid handling evaluation protocols, for example a xe2x80x9cpost-acquisition-rewet-testxe2x80x9d indicates, that during the first part of the combined protocol the fluid acquisition behaviour of the test specimen is studied, whereas the rewet assessment is then carried out in the second part of the test.
A number of such tests have been described, such as in WO 93/02 188 (Guidotti et al.); EP-0 039 974 (Mullane); EP 0 278 601 (Kobayashi); EP 0 539 703 (Hanson).
However, these tests have significant drawback, in so far as they are only sensitive to liquid moisture, which is present in capillaries larger then the capillaries of the pick-up medium. In particular upon development of better absorbent products, it has been found that not only the small amounts of liquid in relatively small pores (i.e. smaller than the pores of the filter pick up paper) can still contribute significantly to the overhydration of the skin of the wearer, but that also the moisture released by the skin itself in the form of sweat can have significant negative effects on overhydration of the skin, such as when covered with an impermeable material. This latter situation is often referred to as xe2x80x9cocclusionxe2x80x9d, and of particular relevance for the non-absorbent regions in the absorbent article, often referred to as xe2x80x9cchassisxe2x80x9d or xe2x80x9cperipheralxe2x80x9d elements.
Another approach to assess the performance of such articles has been proposed by Lask et al. in EP-B-312919, whereby the surface moisture e.g. of an absorbent article is correlated to the reflection and scattering of a light beam. However, also this test is only directed towards the liquid moisture of the surface, andxe2x80x94even if it might have less limitations with respect to capillary size at the lower detection limitxe2x80x94is relying on essentially isotropic and homogeneous properties throughout the topsheet layer.
With improvements in the performance of absorbent articles, the ability of the known methods above to distinguish different products has decreased, such products achieving practically identical performance in said test, even though significant differences were detected by the user of the absorbent articles.
It has now been discovered that absorbent articles can be provided with hitherto unprecedented performance with respect to controlling the impact of the absorbent article on the skin hydration.
This is achieved by relying on a new tool for realistically and efficiently differentiating the absorbent articles with respect to their impact on the skin hydration. This is further achieved by not only focusing on the skin hydration impact of the absorbent article in zones which are either directly loaded with the liquid bodily discharges such as urine, menstrual fluids, or fecal materials of sufficiently high liquid content, but also in the zones of the absorbent article which are generally not being wetted by such liquids.
The present inventions aims at providing a disposable absorbent article covering certain parts of the body of the wearer and comprising distinct areas including a loading area, a storage area and a chassis area, whereby the absorbent article has a Skin Hydration Value of less than 1300, preferably less than 600, more preferably less than 300 as defined by the method described hereinafter; said Skin Hydration Value of the total article reflects the impact of the individual Skin Hydration Values of the respective areas of the articles; the definition of said individual Skin Hydration Value according to methods specific to the area, represents another aspect of the present invention.